1. Field of the Invention
The present invention relates to a dot matrix display apparatus including a number of light emitting elements, and more specifically to an improvement of the dot matrix display apparatus in operation speed and image quality.
2. Description of the Prior Art
Dot matrix display apparatus (called display panel) have widely been used in various fields (e.g. as a panel for indicating Departure and/or Arrival Times of trains or aircraft at stations or airports). In these display panels, light emitting diodes (referred to as LEDs) are available and therefore IC circuits can be incorporated therewith because the LED driving voltage is relatively low. In addition, since LEDs of various colors (red, yellow, green, etc.) have been available, it is possible to realize a large-scale color display panel at a relatively low cost, as compared with the conventional cathode ray tube display apparatus (referred to as CRT).
In these display panels, it is ordinary that external video information signals are once stored in a memory unit and then displayed by activating the LEDs at relatively low speed. Therefore, it has been so far impossible to display images on the basis of video signals at high-speed in real time manner through the display panel configured by LEDs.
Recently, however, there exists a demand of displaying images indicated on a CRT of a personal computer simultaneously on this display panel in real-time fashion. In this case, since computers are usually operated in response to clock signals as high as 14 to 16 MHz, there exists a problem in that the conventional display panels of dot matrix type are not available to display images at high speed, because rise and fall times of LED driving transistors are relatively long as compared with the speed of the clock signal.
The problem involved in the prior-art dot matrix display apparatus will be described in further detail hereinafter with reference to the attached drawings under DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT.